In the food packaging industry, chemical sterilants are employed as bactericidal and sporicidal agents to sterilize food containers. These aseptic containers must have their food contact surfaces thoroughly sterilized to prevent spoilage or contamination of their contents. One of the most suitable chemical sterilants is hydrogen peroxide because of its degradation into oxygen and water, both of which are considered harmless in moderate quantities and which neither taint the food products or render them toxic. Although hydrogen peroxide has been used throughout the world for decades as a chemical sterilant in the aseptic packaging of shelf-stable foods such as milk, fruit juices, soft drinks and other liquid products, it wasn't until 1981 that the U.S. Food and Drug Administration approved its use in the U.S. for aseptic packaging. Foods packaged in hydrogen peroxide sterilized articles must comply with the appropriate FDA Good Manufacturing Practices which include: Part 108 for low acid and acidified foods; Parts 110 and 113 for low acid canned foods; and Part 114 for acidified foods. For example, under its regulations, the FDA set the level of hydrogen peroxide allowable in milk at the time of packaging at one hundred parts per billion, falling to one part per billion within a twenty-four hour time period.
Aseptic packaging is defined as the separate sterilization of the product and the packaging material. The packaging material is formed to a predetermined container configuration. The container is sterilized with a sterilant for a predetermined residence time, then the sterilant is removed from the aseptic container. If the sterilant is hydrogen peroxide at room temperature, then the residence time could be as much as thirty minutes for each container. The long residence time is one of the factors which increases the sterilization time for aseptic containers. The aseptic container is then filled with a desired contents such as milk or juice, and sealed under aseptic conditions. Well known examples of aseptic containers of this type are Tetra Brik.RTM. and Tetra Rex.RTM..
One of the great benefits of aseptic packaging as opposed to conventional packaging is the substantial reduction in the use of energy to refrigerate the food products. For example, conventionally packaged milk is usually stored at temperatures of 4 or 5.degree. C. whereas aseptic packaging allows for storage at room temperature, 25.degree. C. However, this energy savings is partially offset by the energy needed to heat flash off any residual sterilant which may become entrapped in or on the surface of the packaging material. In a monolayer container, a sterilant such as hydrogen peroxide may be present throughout the entire wall of the container. In a multilayer container, the hydrogen peroxide may only be present in a thin surface layer (less than 100 microns thick). In the case of hydrogen peroxide, very high temperatures must be achieved in order to remove any residual hydrogen peroxide. In addition to packaging of foods, aseptic containers can be used for packaging industrial materials in medical, electronic, chemical and mechanical fields such as blood transfusion packs, semiconductor packages, oxidative chemicals packages, precision parts packages and the like. Thus, aseptic containers can be used in various forms in a wide variety of fields.
The packaging industry has failed to invent a way to remove the residual sterilant which would maintain the energy savings and reduce the time for sterilizing aseptic packaging materials. It therefore will be appreciated by those in the packaging industry that there is a substantial need for removal of the residual sterilant in manner that would save energy, reduce sterilizing time and would be cost effective. The present invention fulfills this need and provides other related advantages for the packaging industry.